Asaph Hall (October 15, 1829 – November 22, 1907) was an American astronomer who is most famous for having discovered the moons of Mars (namely Deimos and Phobos) in 1877. He determined the orbits of satellites of other planets and of double stars, the rotation of Saturn, and the mass of Mars. Hall was born in Goshen, Connecticut. Apprenticed to a carpenter at 16, he later enrolled at the Central College in McGrawville, New York. In 1856 he married Angeline Stickney. He and Angeline had 4 sons: Asaph, Jr., Samuel, Angelo, and Percival In 1856, he took a job at the Harvard College Observatory in Cambridge, Massachusetts, and turned out to be an expert computer of orbits. Hall became assistant astronomer at the US Naval Observatory in Washington DC in 1862, and within a year of his arrival he was made professor. In 1875 Hall was given responsibility for the USNO 66-cm/26-in telescope, the largest refractor in the world at the time. It was with this telescope that he discovered Phobos and Deimos. He also noticed a white spot on Saturn which he used as a marker to ascertain the planet's rotational period. In 1884, he showed that the position of the elliptical orbit of Saturn's moon, Hyperion, was retrograding by about 20° per year. Hall also investigated stellar parallaxes and the positions of the stars in the Pleiades cluster. Hall was responsible for apprenticing Henry S. Pritchett at the Naval Observatory in 1875. On June 5, 1872 Hall submitted an article entitled "On an Experimental Determination of Pi" to the journal Messenger of Mathematics. The article appeared in the 1873 edition of the journal, volume 2, pages 113-114. In this article Hall reported the results of an experiment in random sampling that Hall had convinced his friend, Captain O.C. Fox, to perform when Fox was recuperating from a wound received at the Second Battle of Bull Run. The experiment was repetitively throwing at random a fine steel wire onto a plane wooden surface ruled with equidistant parallel lines. Pi was computed as 2ml/an where m is the number of trials, l is the length of the steel wire, a is the distance between parallel lines, and n was the number of intersections. This paper is a very early documented use of random sampling (which Nicholas Metropolis would name the Monte Carlo method during the Manhattan Project of World War II) in scientific inquiry.
Awards and honors
He won the Gold Medal of the Royal Astronomical Society in 1879. Hall crater on the Moon as well as Hall crater on the Martian moon Phobos are named in his honor.
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